Methods have been disclosed to make printing inks suitable for printing either contact lenses or the molds that are then used to make contact lenses. For example, U.S. Pat. No. 4,668,240 to Loshaek discloses colored contact lenses produced by providing a contact lens constructed of polymer and coating at least a portion of the lens with coloring substance, a binding polymer having functional groups, and an additional compound having at least one of —NCO or epoxy. The lens and binding polymers are bonded to each other by the reaction of functional groups.
U.S. Pat. No. 4,857,072 to Narducy, et al. discloses a method for making colored hydrophilic contact lenses. At least a portion of the surface of the lens is coated with a color coat comprising at least one pigment, binding polymer having functional groups, and an additional compound having at least two groups per molecule of —NCO. The coated lens is then subjected to conditions that cause the color coat to adhere to the lens.
U.S. Pat. No. 5,272,010 to Quinn discloses a method for preparation of colored contact lenses similar to that of U.S. Pat. Nos. 4,668,240 and 4,857,072 except that an isocyanate compound is not required. Instead, adhesion promoters such as hexamethoxymethylmelamine are used.
The above-referenced patents (all of which are incorporated herein by reference) are substantially similar in that they all require (a) one or more pigments to add colorant to the contact lens; (b) one or more monomers to help the printing ink bind to the contact lens; (c) an initiator to polymerize the monomers in the printing ink; (d) a binder polymer with appropriate functional groups; and (e) an adhesion promoter to form crosslinks with the functional groups of the binder polymer. The adhesion promoter can also chemically bond the binder polymer to the lens polymer.
However, the methods known in the art have several disadvantages. The first disadvantage concerns the potential use of a diluent in the monomer mixture that is polymerized to make contact lenses. A diluent in the monomer mixture is a well recognized technique for casting contact lenses (U.S. Pat. No. 5,039,459 Larsen-Kindt, et al.). However, a diluent in the monomer mixture and subsequently in the contact lens may interfere with the required crosslinking of the binder polymer. This may be an effect of diluting the concentration of reagents and/or the diluent may react with adhesion promoter to the detriment of the bonding needed to provide adequate adhesion of the colorant to the contact lens. In any case, the capability of the adhesion promoter to provide adequate adhesion of the colorant to the contact lens is diminished.
The second disadvantage of the current processes is related to the requirement that a separate adhesion promoter in the form of a reagent or a specialty, reactive coating be added to the colored lens printing ink. This has all the disadvantages associated with adding an additional ingredient to a manufacturing process.
The third disadvantage is observed in the need for a separate step to react the adhesion promoter to functional groups of the binder polymer. The most commonly described separate step is a thermal cure and this necessitates adding costly equipment to the lens manufacturing process.
The fourth disadvantage is that the printing inks currently used contain a polymerization initiator and monomers that must be polymerized in a post-printing operation.